When should I use RMI-IIOP?

RMI-IIOP is for developers who program in the Java programming language and want to program to the RMI interfaces, but use IIOP as the underlying transport. RMI-IIOP provides interoperability with other CORBA objects implemented in various languages - but only if all the remote interfaces are originally defined as Java RMI interfaces. It is of particular interest to programmers using Enterprise JavaBeans (EJB), since the remote object model for EJB components is based on the RMI API.

RMI-IIOP combines the best features of Java Remote Method Invocation (RMI) with the best features of CORBA. RMI-IIOP speeds distributed application development by allowing developers to work completely in the Java programming language, writing remote interfaces in the Java programming language and implementing them simply using Java technology and the Java RMI APIs.

When using RMI-IIOP to produce technology-based distributed applications written in the Java programming language, there is no separate Interface Definition Language (IDL) or mapping to learn: the remote interfaces can be implemented in any other language that is supported by an OMG mapping and a vendor supplied ORB for that language. Similarly, clients can be written in other languages using IDL derived from the remote Java technology-based interfaces.

RMI-IIOP provides flexibility by allowing developers to pass any Java object between application components either by reference or by value.

Like CORBA, RMI-IIOP is based on open standards defined with the participation of hundreds of vendors and users in the Object Management Group. Like CORBA, RMI-IIOP uses Internet Inter-ORB Protocol (IIOP) as its communication protocol. IIOP eases legacy application and platform integration by allowing application components written in C++, Smalltalk, and other CORBA supported languages to communicate with components running on the Java platform.

What other options do I have for distributed application development?

Developers who program using the Java programming language can choose several solutions for creating distributed applications programs.

Java RMI technology - If all of your applications are written in the Java programming language, you will probably want to use Java RMI technology to enable communication between Java objects on different virtual machines and different physical machines. Using Java RMI technology without its IIOP option leverages its strengths of code portability, security, and garbage collection.
Java IDL technology - Java IDL technology are for CORBA programmers who want to program in the Java programming language based on interfaces defined in CORBA Interface Definition Language (IDL). This is "business as usual" CORBA programming, supporting the Java platform in exactly the same way as other languages like C++ or COBOL.
Enterprise JavaBeans technology - Enterprise JavaBeans (EJB) technology is part of the Java Platform, Enterprise Edition (Java EE). EJB components use the Java RMI/Java IDL technology for their distributed object model, and use the Java Transaction Service (JTS) for their distributed transaction model. When Enterprise JavaBeans components are implemented using the RMI-IIOP protocol for EJB component interoperability in heterogeneous server environments, the standard mapping of the EJB architecture to CORBA enables interoperability with multivendor ORBs, other EJB servers, and CORBA clients written in programming languages other than the Java programming language. For an example application that uses an EJB server with a CORBA client, look at Enterprise JavaBeans Components and CORBA Clients.